Ben, you seem to be concentrating on the least likely suspect: your amplification. If your M3s have "nearly as much low end", something's wrong, and it's unlikely(rather than "definitely")that an amplifier with a higher maximum power rating is the solution.
When I was comparing them it wasn't completely apples to apples. I only had my M3's in the new basement for a very short period of time and hadn't listened to a lot of different things on them before switching out to the M80's. A lot of my experiences and feeling for the M3's have been shaped by the experiences I had with them in my old basement HT where they provided a surprising amount of low end. I realize now that part of my issue with the M80's is my new room. Both in freq response and size (larger).
I need to bring my M3's back downstairs and do a little A-B.